Field of the Invention
The present invention relates generally to an attachment optical system to be detachably mounted between an image pickup optical system and an image pickup apparatus to change a focal length, or an image pickup apparatus, which includes a focal length changing optical system. The present invention relates particularly to an attachment optical system to be used in television cameras for broadcasting, video cameras, digital still cameras, silver film cameras, and the like, which is suitable to change lateral chromatic aberration correction data for digital aberration correction through predetermined computation and transmit the data to the main body of an image pickup apparatus, and an image pickup system, which includes the attachment optical system. The present invention alternatively relates to an image pickup apparatus configured to change, through predetermined computation, lateral chromatic aberration correction data that is obtained from an image pickup optical system, and an image pickup system, which includes the image pickup apparatus.
Description of the Related Art
Attachment optical systems of the related art, which can be mounted onto the image plane side of an image pickup optical system, are mounted when the photographic field of view is to be changed by changing the focal length of the image pickup optical system onto which the attachment optical system is mounted, or when an image is picked up with an image pickup apparatus that is incompatible with the image circle diameter of the image pickup optical system. There is disclosed in Japanese Patent Application Laid-Open No. 2014-170043 a lens that is designed on the premise that the lens is to be used in combination with a color separation prism and that allows the use of a single-chip color camera in combination with a photographing lens for a three-chip camera.
Color image pickup apparatus reproduce a color image by overlaying a channel R (red) image, a channel G (green) image, and a channel B (blue) image on top of one another. When an image of a subject is formed on an image pickup element through an image pickup optical system, a phenomenon occurs in which images of the channels R, G, and B are shifted with one another due to a lateral chromatic aberration of a lens. Various methods have been proposed to correct the shift electrically. A replacement lens suitable for lens-replaceable systems is disclosed in Japanese Patent No. 5279934.
In Japanese Patent Application Laid-Open No. S62-194787, there is disclosed a color television camera that uses a lens with a built-in extender function to shift the focal length. The camera disclosed in Japanese Patent Application Laid-Open No. S62-194787 does not need to reset the distortion correction amount each time extender settings are switched because a distortion correction amount optimum for the extender switching state is output to make an adjustment with respect to a subject for which image pickup conditions change constantly, and switching extender settings does not break the adjusted state prior to the switching.
The lateral chromatic aberration of an image pickup optical system changes when a focal length changing optical system, such as an attachment optical system, is mounted onto the image pickup optical system. This gives rise to a problem in that lateral chromatic aberration is not corrected satisfactorily, or even worsens in some cases, when lateral chromatic aberration correction data that is stored in an image pickup optical system in advance is used as it is to make a digital aberration correction in a system where a focal length changing optical system is mounted onto the image pickup optical system.